Electrical components typically require the application of electrical power in order to operate correctly. In an electronic control module as utilized to control an internal combustion engine, such power need not be perpetually applied since the engine to be controlled will typically not operate continually. During nonoperation of the engine, such electronic control modules can be powered down to avoid depleting the power source.
To provide this flexibility, one could simply place a switch between the power source and the electronic component to be powered. Unfortunately, this simple solution gives rise to a number of problems. For instance, electronic control modules as mentioned above typically include a microprocessor. Microprocessors ordinarily require a short period of time during which a power down can be correctly instituted. During this period, the microprocessor will often store data in nonvolatile memory and perform other functions to assure a trouble free power up operation.
A simple switch to disconnect power from such a microprocessor will not necessarily allow these functions to be correctly implemented. In addition, such a switch does nothing to protect the microprocessor or other powered components from the problems that can result by incorrectly connecting the power source to the powered component, such as by reversing the polarity of the power source, or by incorrectly applying an over voltage to the powered components. In either of these cases, a simple switch will likely allow the powered components to be temporarily inhibited or permanently disabled.
One prior art attempt to avoid these problems can be seen in FIG. 1. In this prior art structure, a power source (A) connects to a microprocessor (B) through a first switch (C). The first switch (C) can be controlled by either of two switches, an ignition switch (D) or a microprocessor controlled switch (E). The ignition switch (D) can be closed to apply power from the power source (A) to the control input of the first switch (C), thereby causing the first switch (C) to close and apply power from the power source (A) to the microprocessor (D). Once the microprocessor (B) has begun normal operation, the microprocessor (B) can close the microprocessor controlled switch (E) and thereby provide its own control signal to the first switch (C).
The microprocessor (B) also has means (F) to determine whether the ignition switch (D) remains closed or open. Upon opening the ignition switch (D), the microprocessor (B) enters a power down phase and attends to its various power down functions. Once these are completed, the microprocessor terminates its control signal to the microprocessor controlled switch (E). The first switch (C) then opens and uncouples the microprocessor (B) from the power source (A). Under normal operating conditions this prior art structure did not have a quiescent voltage drain.
This structure did not resolve all of the problems set forth above. Further, there were no specific assurances that the system described would actually power down unless other precautions were taken, such as providing watch dog circuits or the like.
There therefore exists a need for a power distribution device that can be reliably and economically utilized to selectively connect and disconnect a power source from one or more electrical components as desired. Such a device should not impose a voltage drain on the power source during its quiescent operating mode. In addition, such a device should have means for providing an adequate but determinate delay period when decoupling power to ensure that a microprocessor will have adequate time to effectuate a controlled power down. Further, such a device should provide both over voltage protection and protection against an application of a reverse biased power source.
These needs and others are substantially met through provision of the power distribution device described in this specification. This device includes generally a first input for operably connecting to a power source, a second input for operably connecting to a switch, and an output for operably connecting to the electrical components to be powered. The device also includes a first unit for sensing when the operator controlled switch has a predetermined conductive state, and a second unit that can respond to the first unit to provide a control signal. A power switch unit responds to this control signal to selectively connect or disconnect the device output from the power source input.
Finally, the device includes a delay unit for delaying the response of the second unit to a change in the output signal state of the first unit.
In one embodiment of the device, the first unit can be provided through use of a comparator having both inputs connected to sense the conductive state of the operator controlled switch. The second unit can also be implemented by use of a comparator, with this comparator connected to sense the output of the first comparator.
The power switch unit can be implemented through use of a transistor having its base connected to the output of the second comparator and its power terminals connected in series with the coil of a relay switch. The relay switch can thereby be manipulated to selectively connect and disconnect the power source input from the device output.
The delay unit can be comprised of a capacitor that operably connects between the output of the first comparator and the pertinent input of the second comparator.
Upon closing the operator controlled switch, the two comparator units power up. The first comparator then senses the closed state of the switch and provides an output signal. This output signal causes the second comparator unit to provide a drive signal to the power switch unit, thereby causing the relay associated therewith to close. Closing of the relay switch then connects the device output to the power source input.
Upon opening the operator controlled switch, the output of the first comparator will fall low. The delay unit capacitor, however, continues to provide an input signal to the second comparator for a specific duration of time. During this duration of time, the second comparator will continue to drive the power switch unit to enable a microprocessor connected to the device output to power down in an appropriate manner.
When the delay unit capacitor has become discharged, the second comparator output will go low, thereby allowing the power switch unit relay to open and disconnect power from the powered components.
The device also includes overvoltage protection. A Zener diode has been provided that will break down and conduct at a specified overvoltage level or above and cause a switch to close that will effectively inhibit the power switch unit such that the relay cannot be opened or maintained in a closed configuration.
The device also includes reverse voltage protection in the form of a plurality of diodes that are positioned to prevent an application of reverse biased voltage to the device circuitry. In this way, both the circuitry of the device itself, and the components of the supplied system, will be protected.